Caisson structures and methods for precisely and stably sinking the caisson structures into ground

ABSTRACT

A caisson structure including enclosed well walls with internal surfaces and external surface placed opposite to the internal surfaces is provided. A plurality of frame beams are provided between the internal surfaces and mutually intersected in a horizontal plane and a vertical plane. A bottom frame beam is provided close to a lowest end of the well walls. The internal surfaces are provided with internal support blocks at a first height, and the external surfaces are provided with external support blocks at a second height, with the second height greater than the first height. A bottom surface of the bottom frame beam is a plane without cutting edges, and the lowest end of the well walls is formed with cutting edges having an inclined surface. A method of sinking the caisson structure into the ground exactly is also provided.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims the benefits of priority of Chinese application number 200810026012.6, entitled CAISSON STRUCTURES AND METHODS FOR PRECISELY AND STABLY SINKING THE CAISSON STRUCTURES INTO GROUND, and filed in the name of Cixin, DING and Shudong, DING on Jan. 24, 2008. The entire content of the application is incorporated herein by reference.

FIELD OF THE INVENTION

The present application relates to an architectural structure, in particular to a caisson structure and a method for stably sinking the caisson structure into ground to achieve a precise final sinking.

BACKGROUND OF THE INVENTION

Caissons, also known as open caisson or sinking well, are architectural structures used as deep foundation support for such as underground space building or high-rise building, and have a unique application range. For example, caissons may not be used in a hard enough soil environment where it may be convenient and economic to use a foundation pit construction technique other than the caisson technique. However, it will be preferred to use the caisson technique in a soft soil environment, because if conventional support structures are used, the porous and unstable soil can cause a sharp increase of costs, prolong the sinking period and put workers at a higher sinking risk.

Thus, caissons are widely used in alluvium environment such as close to rivers, lakes or seas. However, when a caisson is used in a soft soil foundation, serious accidents, such as sudden sinking, over sinking, center deviation, plane rotation, slant-wise sinking, distortion and cracking, soil pouring into the well and outside collapse, can easily happen due to improper design or operation. These are mainly caused by the intrinsic deficiency in vertical plan stiffness or minimum vertical profile torsional stiffness of some sections of the caisson. These are also caused by the current caisson structures and the sinking methods used, which cannot insure, in the sense of engineering, a stable and accurate sinking Consequently, most of caissons are rocky during sinking which can easily cause accidents. Thus, it has to rectify the caisson during the course of sinking so as to keep balance. This makes the sinking work more difficult, prolongs the sinking period and increases the sinking costs. For a long time past, many efforts have been made to overcome these disadvantages in associate with the conventional techniques but without success.

Currently, caisson having the maximum area can only meet the requirements of middle-scale foundation pits. It is difficult in the art to construct a caisson having a larger area, diameter (for circular caisson), length or width (for rectangular caisson) or inner lattice, or having more complex abnormal and asymmetric shape. This is due to the intrinsic deficiency of stiffness of the caisson. The intrinsic deficiency of stiffness restricts the development of caisson towards greater size, lower cost and more complexity, and in turn, limits the use of caisson.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a caisson structure which is not prone to deform or break and having a lower requirement on the stiffness of the caisson itself, so as to improve safety during sinking.

It is another object of the present invention to provide a method for stably and precisely sinking a caisson structure into ground. The method is used to ensure sinking in a controllable manner and to achieve an accurate final sinking. Thus, serious accidents that can easily happened in conventional techniques, such as sudden sinking, over sinking, center deviation, plane rotation, slant-wise sinking, distortion and cracking, soil pouring into the well and outside collapse, can be avoided.

To achieve the above objects, it is provided a caisson structure including enclosed well walls with internal surfaces and external surface placed opposite to the internal surfaces. A plurality of frame beams are provided between the internal surfaces and mutually intersected in a horizontal plane and a vertical plane. A bottom frame beam is provided close to a lowest end of the well walls. The internal surfaces are provided with internal support blocks at a first height, and the external surfaces are provided with external support blocks at a second height, with the second height greater than the first height. A bottom surface of the bottom frame beam is a plane without cutting edges, and the lowest end of the well walls is formed with cutting edges having an inclined surface.

In another aspect, the present invention provides a method for stably and precisely sinking a caisson structure into ground and achieve an accurate final sinking, comprising steps of:

(a) selecting a sinking area, and driving support piles into the ground within the area with a length of the support piles exposed above the ground;

(b) constructing a caisson structure within the area, the caisson structure including enclosed well walls with internal surfaces and external surface placed opposite to the internal surfaces, a plurality of frame beams being provided between the internal surfaces and mutually intersected in a horizontal plane and a vertical plane, a bottom frame beam being provided close to a lowest end of the well walls, the internal surfaces being provided with internal support blocks at a first height, and the external surfaces being provided with external support blocks at a second height, with the second height greater than the first height, and a bottom surface of the bottom frame beam being a plane without cutting edges, the bottom frame beam and the internal support blocks being supported by a group of internal support piles through internal hoisting jacks, the external support blocks being supported by a group of external support piles through a group of sets of heel blocks with one above another in vertical direction and external hoisting jacks located below nethermost heel blocks, position-limiting devices being provided surround each set of heel blocks so that the heel blocks are only movable in vertical direction, the first and second hoisting jack each comprising a base and a pusher movable within the base for a specific distance, the pusher being initially in a condition of extending out, each pusher of the hoisting jacks being fixed at a top end thereof to the internal support block and the bottom frame beam and suspended there below, all the hoisting jacks being divided into a first group and a second group which are staggered for description purpose;

(c) operating all the hoisting jacks to make the pushers move back into the bases for a predetermined distance, and keep a remaining stroke of at least 30 mm in length, so that the caisson undergoes a first sinking for the predetermined distance within the sinking area, and the cutting edges of the well walls insert into the ground;

(d) operating the first group of the hoisting jacks to make the pushers move for a length of 20 to 50 mm back into the bases, so that the second group of the hoisting jacks support the whole load of the caisson, while the first group is load-free, then removing the highest heel blocks of the sets of heel blocks between the external support blocks and the corresponding external hoisting jacks, followed by operating each external hoisting jack in the first group to make each pusher extend out further in relative to the base until the remaining heel blocks are in tight contact with the external support block, cutting off a length of the internal support piles below the internal hoisting jacks in the first group, so as to form a gap between the bases of the internal hoisting jacks in the first group and the internal support piles that are cut, operating the internal hoisting jacks in the first group to lower the bases of the internal hoisting jacks until the bases are in tight contact with top ends of the internal support piles that are cut, so that the first group and the second group of the hoisting jacks support the caisson together;

(e) operating the second group of the hoisting jacks to make the pushers move for a length of 20 to 50 mm back into the bases, so that the first group of the hoisting jacks support the whole load of the caisson, while the second group is load-free, then removing the highest heel blocks of the sets of heel blocks between the external support blocks and the corresponding external hoisting jacks, followed by operating each external hoisting jack in the second group to make each pusher extend out further in relative to the base until the remaining heel blocks are in tight contact with the external support block, cutting off a length of the internal support piles below the internal hoisting jacks in the second group, so as to form a gap between the bases of the internal hoisting jacks in the second group and the internal support piles that are cut, operating the internal hoisting jacks in the second group to lower the bases of the internal hoisting jacks until the bases are in tight contact with top ends of the internal support piles that are cut, so that the first group and the second group of the hoisting jacks support the caisson together;

(f) removing the position-limiting devices surrounding the external hoisting jacks;

(g) operating all the hoisting jacks to make the pushers move back into the bases for another predetermined distance, and keep a remaining stroke of at least 30 mm in length, so that the caisson undergoes a second sinking for the another predetermined distance within the sinking area;

(h) digging away a layer of soil in the bottom of the caisson to expose the internal support piles;

(i) repeating steps (d) to (h) such that the caisson sinks gradually into the ground until the heel blocks on each external hoisting jack are removed and each external hoisting jack directly supports the corresponding external support block;

(j) operating all the hoisting jacks to make the pushers move fully back into the bases, such that the caisson sinks to a predetermined depth;

(k) removing the hoisting jacks, and casting cap concrete on the top of the support piles until the caisson is supported completely by cap concrete, achieving an accurate final sinking

The advantages of the present invention reside in that: the requirements on the self stiffness of the caisson are greatly reduced due to the presence of many support blocks and the use of support piles and hoisting jacks evenly distributed under the caisson, the caisson is thus not prone to deform or break, so that the sinking safety is improved. In addition, the caisson can be stably and precisely sinked to the predetermined depth in the ground in a controllable manner through the mutual cooperation between the support blocks and the hoisting jacks, so that serious accidents that can easily happened in conventional techniques, such as sudden sinking, over sinking, center deviation, plane rotation, slant-wise sinking, distortion and cracking, soil pouring into the well and outside collapse, can be avoided.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a top view of a caisson of the present invention, illustrating the positions of all the support piles distributed in the plane of the caisson and the cooperation between the support piles and the caisson.

FIG. 2 is a front view of the caisson shown in FIG. 1, showing the cooperation between the external support blocks of the external wall surfaces and heel blocks, and corresponding pipe piles driven to the ground.

FIG. 3 is a sectional view of the caisson shown in FIG. 1 along line B-B, showing the cooperation between cutting edges and the ground, and the cooperation between the bottom frame beam inside the caisson and the corresponding pipe piles driven into the ground.

FIG. 4 is a sectional view of the caisson in FIG. 1 along line A-A.

FIG. 5 is a sectional view of the caisson in FIG. 1 along line C-C.

FIG. 6 is a partial view showing the position relationship among some of the external support blocks, heel blocks, hoisting jacks and pipe piles driven into the ground shown in FIG. 2.

FIG. 7 is a sectional view of the caisson in FIG. 6 along line E-E.

FIG. 8 is a sectional view of the caisson in FIG. 6 along line D-D.

FIG. 9 is a perspective view of the guiding rail shown in FIG. 8.

FIG. 10 is a top view of one heel block shown in FIG. 6.

FIG. 11 is a perspective view of the position-limiting plate shown in FIG. 6.

FIGS. 12 a to 12 d show the changes of the external support blocks, heel blocks, hoisting jacks and corresponding pipe piles during the sinking of the caisson.

FIGS. 13 a to 13 d show the changes of the external support blocks, heel blocks, hoisting jacks and corresponding piles, and also the changes of the hoisting jacks below the bottom frame beam and the pipe piles supporting the hoisting jacks, during the sinking of the caisson.

FIG. 14 illustrates the device for taking soil out of the caisson and a plan view of the arrangement of the caisson.

FIG. 15 illustrates the device for taking soil out of the caisson and a perspective view of the arrangement of the caisson.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The present invention will be described in greater detail and in reference to accompanied drawings.

The structure of the caisson will be described first. Referring to FIGS. 1 to 11, caisson 100 is in general of a rectangular shape, and has, for example, a reinforced concrete structure or steel structure. Caisson 100 includes four well walls 102 connected to form an enclosed structure. Any two of the four well walls 102 are parallel with each other, such that the well walls form a rectangular structure. Each well wall 102 has an internal surface 110 and an external surface 108 opposite to the internal surface. A plurality of frame beams is provided between internal surfaces of any two opposite well walls and these frame beams are mutually intersected in both a horizontal plane and a vertical plane. For example, a longitudinal frame beam 104 is formed between two laterally arranged well walls. Similarly, a lateral frame beam 106 is formed between two longitudinally arranged well walls. Longitudinal frame beam 104 and Lateral frame beam 106 are orthogonal to each other, so as to provide structure strength in horizontal direction for caisson 100.

The longitudinal and lateral frame beams located undermost (closest to the ground) constitute bottom horizontal frame beam 126 (see FIG. 3). Frame beam 126 is used to partly support caisson 100 during sinking

Each frame beam is fixed to well wall 102 via a frame pillar 116 provided on internal surface 110 of well wall 102. In addition, when necessary, internal partition walls 124 can be arranged between frame beams, so as to further enhance the overall structure strength of the caisson 100.

In particular, a plurality of external support blocks 112 is provided on each external surface 108 of well walls 102 close to the top end of the caisson 100. External support blocks 112 have the same height (a first height) in relative to the bottom of the caisson. Similarly, a plurality of internal support blocks 114 is provided on each internal surface 110 of well walls 102 close to the top end of caisson 100. Internal support blocks 114 have the same height (a second height) in relative to the bottom of the caisson. Particularly, the second height is much greater in value than the first height. The requirements on the stiffness of the caisson is greatly reduced due to the presence of the external and internal support blocks and with the aid of the support piles and hoisting jacks evenly distributed below the caisson. In other words, it is not necessary for the sectional plane of the caisson to be very large to ensure safety of sinking and usage of the caisson. Referring to FIGS. 3 and 5, cutting edge 128 having an inclined surface is formed at the bottom of each well wall 102. Cutting edge 128 facilitates the sinking of caisson 100 due to the sharp edge thereof.

The method for precisely sinking the caisson into the ground is described hereinafter. Supporting members in relative to the method is first discussed. Referring to FIGS. 2, 3 and 5, in order to stably support the caisson on the ground, a predetermined amount of support piles, such as pipe piles 118, are driven into the ground 300 (see FIG. 5). Preferably, pipe piles 118 are driven into the ground to contact with bedrock bearing stratum 200 (see FIG. 5). The number and distribution of pipe piles 118 is dependent on the structure of the caisson and the geological condition. In this example, pipe piles 118 are driven into the ground 300 with a length of the piles exposed above the ground. Pipe piles 108 are located below the junction of any two bottom frame beams (i.e., longitudinal frame beam and lateral frame beam) and positions corresponding to external support blocks 112 and internal support blocks 114. In addition, pipe piles 108 are also located below bottom frame beams 126 (see FIG. 3). In FIGS. 1 and 2, the open circles and closed circles indicate the distribution of the pipe piles. The evenly distributed pipe piles play a very important role in the stable and accurate sinking of caisson 100.

Hoisting jacks 120 for adjusting the height of the caisson are provided between the underground portion of pipe piles 108 and internal support blocks 114 (see FIG. 5). Similarly, hoisting jacks 120 for adjusting the height of the caisson are provided between the underground portion of pipe piles 108 and bottom frame beams 126 (see FIG. 3). Hoisting jacks 120 are also provided between the underground portion of pipe piles 108 and external support blocks 112, and between hoisting jacks 120 and the external support blocks 112 is provided heel blocks 122 (see FIGS. 2 and 5). The top ends of the hoisting jacks in the well are fixed to the corresponding portions above the hoisting jacks.

The relative positions between external support blocks 112 and hoisting jacks 120 and between heel blocks 122 and pipe piles 118 are described as below. Referring to FIGS. 6 to 11 and FIG. 1, external support blocks 112 protrude outward from external surface 108 of well wall 102. Each external support block 112 has a base 160 protruded outward from external surface 108 and two position-limiting walls 134 extended downward from base 160. Base 160, said two position-limiting walls 134 and external wall 108 define a semi-enclosed space. A hollow rectangular guiding rail 130 is disposed in the space, and rectangular heel blocks 122 are contained between guiding rail 130 and said two position-limiting walls 134. In addition, two position-limiting walls 134 are connected to each other via a position-limiting plate 132. Heel blocks 122 are thus contained within a space defined by two position-limiting walls 134, guiding rail 130 and position-limiting plate 132, such that heel blocks 122 will not fall at the sides during sinking Said two position-limiting walls 134, guiding rail 130 and position-limiting plate 132 constitute the position-limiting device of the present invention. Hoisting jack 120 can be any jack known in the art. Hoisting jack 120, for example, includes a base portion 504 and a pusher 502 movable within the base for a specific distance by use of a handle (not shown). It should be noted that, position-limiting walls 134 extend vertically along the overall height of caisson 100. Moreover, position-limiting walls 134 are temporary structures which are cut short gradually when the heel blocks are removed one by one during sinking. The position-limiting walls 134 will completely cut away when all the heel blocks are removed.

It should be noted that, the present invention is not limited to the rectangular caisson as set forth above. In contrast, caissons with other shapes, such as circular caisson, square caisson, regular polygon caisson and various asymmetric polygons caissons can also be a part of the invention.

The method of the present invention is carried out based on the alternation of the load of the caisson between support piles and the height adjustability of the hoisting jacks. FIGS. 12 a to 13 d show the processes of the present method. Referring first to FIGS. 12 a and 13 a, showing the initial status of the outside and inside of the caisson, respectively. A predetermined number of pipe piles 118 are firstly driven into the ground, so that caisson 100 is supported thereon. Specifically, external support blocks 112 are supported by pipe pile 118 through a plurality of heel blocks 122 and hoisting jacks 120 between the corresponding pipe pile 118 and the lowest heel block 122. The bottom frame beam 126 in caisson 100 is supported by pipe pile 118 directly through hoisting jacks 120. Also, the internal support blocks in caisson 100 are supported by the pipe pile 118 directly through hoisting jacks 120 (see FIG. 5). In this case, the weight (load) of caisson 100 is distributed on all the pipe piles (outside and inside of the caisson). In other words, all the pipe piles together receive the weight of caisson 100. All the hoisting jacks at this moment are in extended condition, that is, pusher 502 in each jack 120 is at the highest position. Cutting edges 128 of caisson 100 are initially inserted into the ground. For purpose of description only, the hoisting jacks are divided into two groups that are staggered with each other. The first group is indicated by the closed circle shown in FIG. 1, and the second group is indicated by the open circle shown in FIG. 1.

As shown in FIGS. 12 b and 13 b, operating all the hoisting jacks to withdraw the pusher for a predetermined distance. Caisson 100 sinks for the same distance due to the lowering of pusher 502, so that the cutting edges are inserted into the ground for a further distance and the caisson compact the below soil to enhance the horizontal fixation effect of the foundation soil, and in turn, the stability of caisson 100. Also, the foundation soil receives part of the weight of the caisson, so that the load to the hoisting jacks is reduced.

FIGS. 12 c and 13 c show the subsequent operation of the method. To facilitate description, heel blocks 122 outside the well wall are numbered from top to bottom with numeric value 1, 2, 3 . . . . Referring to FIGS. 6 to 11, the first group of hoisting jacks (comprising external and internal hoisting jacks) is lowered for a predetermined distance, such as 30 to 50 mm, and the uppermost heel block (No. 1) is removed from two position-limiting walls 134 of external support blocks 112. Immediately after that, operating the external hoisting jacks in the first group to rise and contact with the heel block No. 2. The No. 2 block is now in contact with external support block 112.

Next, cutting away a length of the internal pipe piles (pipe piles supporting the internal hoisting jacks, also referred as to internal support piles) at each top end. Then, rising the pusher of the internal hoisting jacks in the first group to support the parts between the bottom frame beam (or the internal support blocks) and the internal pipe piles. At this moment, the whole weight of the caisson covers on both the first and the second group of the hoisting jacks. Subsequently, cutting away a portion of the position-limiting walls 134 at the bottom end, in order to avoid any obstacle caused by the bottom end during sinking

The second group of hoisting jacks (comprising external and internal hoisting jacks) is lowered for a predetermined distance, such as 30 to 50 mm, and removes the uppermost heel block (No. 1) from two position-limiting walls 134 of external support blocks 112. Immediately after that, operating the external hoisting jacks in the second group to rise and contact with the heel block No. 2. The No. 2 block is now in contact with external support block 112. Next, cutting away a length of the internal pipe piles (pipe piles supporting the internal hoisting jacks, also referred as to internal support piles) at each top end. Then, rising the pusher of the internal hoisting jacks in the second group to support the parts between the bottom frame beam (or the internal support blocks) and the internal pipe piles. At this moment, the whole weight of the caisson covers on both the first and the second group of the hoisting jacks, and the heel block No. 1 on the external support block is removed. In the mean time, all the internal support piles are cut away a predetermined length. Subsequently, cutting away a portion of the position-limiting walls 134 at the bottom end, in order to avoid any obstacle caused by the bottom end during sinking

As shown in FIGS. 12 d and 13 d, the pushers of the external and internal hoisting jacks 120 are lowered, so that caisson 100 is lowered for another distance.

The processes described in reference to FIGS. 12 c and 13 c are repeated except that the heel block No. 2 is removed. The processes are repeated until all the heel blocks are removed and the whole position-limiting walls are cut away. The external and internal hoisting jacks are operated to withdraw the pushers gradually back to the base, and the caisson sinks to the predetermined depth. At last, the hoisting jacks are removed, and cap concrete is cast on the top of the support piles until the caisson is supported completely by the cap concrete, so as to achieve an accurate final sinking

During operation, the internal pipe piles are cut away gradually. However, most portions of the pipe piles are embedded in the ground. Thus, soil around the pipe piles in the ground should be dug out. This is achieved with the aid of twin beam bridge gantry crane 500 and belt conveyer 600 used therewith shown in FIGS. 14 and 15. Crane 500 and belt conveyer 600 are placed on the top of caisson 100. The soil can be easily dug out because of the lattice structure of the caisson. In addition, an excavator can be placed in the caisson by crane 500.

Generally, the caisson structure provided by the present invention includes enclosed well walls with internal surfaces and external surface placed opposite to the internal surfaces. A plurality of frame beams are provided between the internal surfaces and mutually intersected in a horizontal plane and a vertical plane. A bottom frame beam is provided close to a lowest end of the well walls. The internal surfaces are provided with internal support blocks at a first height, and the external surfaces are provided with external support blocks at a second height, with the second height greater than the first height. A bottom surface of the bottom frame beam is a plane without cutting edges, and the lowest end of the well walls is formed with cutting edges having an inclined surface.

Preferably, the external support blocks include a base and a pair of position-limiting walls extending downward at the base. The base and the position-limiting walls extend vertically along the height direction of the well walls. A rectangular guiding rail is disposed within the position-limiting walls.

The method of the present invention comprises step of:

(a) selecting a sinking area, and driving support piles into the ground within the area with a length of the support piles exposed above the ground;

(b) constructing a caisson structure within the area, the caisson structure including enclosed well walls with internal surfaces and external surface placed opposite to the internal surfaces, a plurality of frame beams being provided between the internal surfaces and mutually intersected in a horizontal plane and a vertical plane, a bottom frame beam being provided close to a lowest end of the well walls, the internal surfaces being provided with internal support blocks at a first height, and the external surfaces being provided with external support blocks at a second height, with the second height greater than the first height, and a bottom surface of the bottom frame beam being a plane without cutting edges, the bottom frame beam and the internal support blocks being supported by a group of internal support piles through internal hoisting jacks, the external support blocks being supported by a group of external support piles through a group of sets of heel blocks with one above another in vertical direction and external hoisting jacks located below nethermost heel blocks, position-limiting devices being provided surround each set of heel blocks so that the heel blocks are only movable in vertical direction, the first and second hoisting jack each comprising a base and a pusher movable within the base for a specific distance, the pusher being initially in a condition of extending out, each pusher of the hoisting jacks being fixed at a top end thereof to the internal support block and the bottom frame beam and suspended there below, all the hoisting jacks being divided into a first group and a second group which are staggered for description purpose;

(c) operating all the hoisting jacks to make the pushers move back into the bases for a predetermined distance, and keep a remaining stroke of at least 30 mm in length, so that the caisson undergoes a first sinking for the predetermined distance within the sinking area, and the cutting edges of the well walls insert into the ground;

(d) operating the first group of the hoisting jacks to make the pushers move for a length of 20 to 50 mm back into the bases, so that the second group of the hoisting jacks support the whole load of the caisson, while the first group is load-free, then removing the highest heel blocks of the sets of heel blocks between the external support blocks and the corresponding external hoisting jacks, followed by operating each external hoisting jack in the first group to make each pusher extend out further in relative to the base until the remaining heel blocks are in tight contact with the external support block, cutting off a length of the internal support piles below the internal hoisting jacks in the first group, so as to form a gap between the bases of the internal hoisting jacks in the first group and the internal support piles that are cut, operating the internal hoisting jacks in the first group to lower the bases of the internal hoisting jacks until the bases are in tight contact with top ends of the internal support piles that are cut, so that the first group and the second group of the hoisting jacks support the caisson together;

(e) operating the second group of the hoisting jacks to make the pushers move for a length of 20 to 50 mm back into the bases, so that the first group of the hoisting jacks support the whole load of the caisson, while the second group is load-free, then removing the highest heel blocks of the sets of heel blocks between the external support blocks and the corresponding external hoisting jacks, followed by operating each external hoisting jack in the second group to make each pusher extend out further in relative to the base until the remaining heel blocks are in tight contact with the external support block, cutting off a length of the internal support piles below the internal hoisting jacks in the second group, so as to form a gap between the bases of the internal hoisting jacks in the second group and the internal support piles that are cut, operating the internal hoisting jacks in the second group to lower the bases of the internal hoisting jacks until the bases are in tight contact with top ends of the internal support piles that are cut, so that the first group and the second group of the hoisting jacks support the caisson together;

(f) removing the position-limiting devices surrounding the external hoisting jacks;

(g) operating all the hoisting jacks to make the pushers move back into the bases for another predetermined distance, and keep a remaining stroke of at least 30 mm in length, so that the caisson undergoes a second sinking for the another predetermined distance within the sinking area;

(h) digging away a layer of soil in the bottom of the caisson to expose the internal support piles;

(i) repeating steps (d) to (h) such that the caisson sinks gradually into the ground until the heel blocks on each external hoisting jack are removed and each external hoisting jack directly supports the corresponding external support block;

(j) operating all the hoisting jacks to make the pushers move fully back into the bases, such that the caisson sinks to a predetermined depth;

(k) removing the hoisting jacks, and casting cap concrete on the top of the support piles until the caisson is supported completely by the cap concrete, achieving an accurate final sinking

Specifically, the external support blocks include a base and a pair of position-limiting walls extending downward at the base. The base and the position-limiting walls extend vertically along the height direction of the well walls. A rectangular guiding rail is disposed within the position-limiting walls. The heel blocks are disposed in a space defined by the base, the position-limiting walls and the guiding rail. The two position-limiting walls are connected to each other via a position-limiting plate. The position-limiting walls, the guiding rail and position-limiting plate constitute the position-limiting device of the present invention. The support pile may be high strength concrete pipe pile or steel pipe pile, and the pipe piles should be driven into the bedrock bearing stratum.

The caisson can be stably and precisely sinked to the predetermined depth in the ground in a controllable manner through the mutual cooperation between the support blocks and the hoisting jacks, so that serious accidents that can easily happened in conventional techniques, such as sudden sinking, over sinking, center deviation, plane rotation, slant-wise sinking, distortion and cracking, soil pouring into the well and outside collapse, can be avoided.

The external and internal support blocks may be reinforced concrete structure or steel structure. The support blocks can be separate blocks, ring beam blocks or crown cantilever blocks. In addition, the hoisting jack can be any other mechanical lifting members without limiting to the structures provided in the present application. The external support blocks, internal support blocks, bottom frame beams can be used separately or in together, dependent on the designs of the caisson structures. In addition, the present methods can be used in caissons with larger area, more complex abnormal and asymmetric shapes or larger dimensions, and it can be used in a more soft soil environment. The methods are cost effective compared to the conventional methods. 

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 7. A support system for sinking a caisson structure, the caisson structure including enclosed well walls, wherein the support system includes: a plurality of support piles vertically inserted into the ground, said caisson structure is located above the plurality of support piles; and a plurality of mechanical lifting members located between the support piles and the caisson structure, with one support pile corresponding to one mechanical lifting member.
 8. The support system of claim 7, wherein the caisson structure further includes frame beams located in and fixed to the well walls, the support piles being located on inner side of the well walls, the mechanical lifting members supporting bottom surfaces of the frame beams in the caisson structure.
 9. The support system of claim 7, wherein internal surfaces of the well walls of the caisson structure is provided with internal support blocks close to the bottom of the caisson structure and protruding inward and perpendicularly to the internal surfaces, the support piles being located on inner side of the well walls, the mechanical lifting members supporting the internal support blocks.
 10. The support system of claim 7, wherein the support piles is located on outer side of the well walls, external surfaces of the well walls of the caisson structure being provided with external support blocks, and the external support blocks comprising a base portion and a pair of position-limiting walls extending downward at the base portion, a plurality of heel blocks being provided in the position-limiting walls with one heel block above another, lowest heel blocks being in contact with the top ends of the mechanical lifting members.
 11. The support system of claim 10, wherein a guiding rail is provided between the position-limiting walls and fixed to one of the external surfaces of the well walls.
 12. The support system of claim 11, wherein a position-limiting plate is provided outside the position-limiting walls, the position-limiting plate, the position-limiting walls and the guiding rail constituting a position-limiting device enabling the heel blocks to move only in a vertical direction.
 13. A method for precisely sinking a caisson structure into ground, comprising steps of: (a) selecting a construction area, and driving support piles into the ground within the area with a length of the support piles exposed above the ground; (b) placing a mechanical lifting member on each support pile, these mechanical lifting members being initially in a extended position; (c) placing a caisson structure on the mechanical lifting members, said caisson structure including enclosed well walls, the support piles being located on the inner side of the well walls; (d) operating each mechanical lifting member to retract for a first distance, so that the caisson structure is sinked for the same distance; (e) separating all the mechanical lifting members into a first group and a second group which are staggered, operating the first group to retract for a second distance, so that the second group receiving the whole load of the caisson structure, cutting away at its top end a length of each support file under the first group of the mechanical lifting members, operating the first group to extend to support between the caisson structure and the support piles, then operating the second group to retract for a third distance, so that the first group receiving the whole load of the caisson structure, cutting away at its top end another length of each support file under the second group of the mechanical lifting members, operating the second group to extend to support between the caisson structure and the support piles; (f) repeating steps (d) and (e) until the caisson structure is sinked to a predetermined position; (g) operating the first group to retract for a forth distance so that the second group receiving the whole load of the caisson structure, then taking out the first group and casting cap concrete between the caisson structure and the support piles under the first group of the mechanical lifting members, and operating the second group to retract for a fifth distance so that the cap concrete receiving the whole load of the caisson structure, then taking out the second group and casting another amount of cap concrete between the caisson structure and the support piles under the second group of the mechanical lifting members.
 14. The method of claim 13, wherein in the step (c) frame beams are provided to fix to the well walls, so as to support the frame beams at the bottom by the support piles, and thus in the step (g) the cap concrete is cast between the frame beam and the support files.
 15. The method of claim 13, wherein in the step (c) internal support blocks are provided on internal surfaces of the well walls close to the bottom of the caisson structure, the internal support blocks extending inward and perpendicularly to the internal surfaces, and the mechanical lifting members been supported by the support piles.
 16. A method for precisely sinking a caisson structure into ground, comprising steps of: (a) selecting a construction area, and driving support piles into the ground within the area with a length of the support piles exposed above the ground; (b) placing a mechanical lifting member on each support pile, these mechanical lifting members being initially in a extended position; (c) placing a caisson structure on the mechanical lifting members, said caisson structure including enclosed well walls, the support piles being located on the outer side of the well walls, providing external support blocks on external surfaces of the well walls, the external support blocks comprising a base portion and a pair of position-limiting walls extending downward at the base portion, a plurality of heel blocks being provided in the position-limiting walls with one heel block above another, lowest heel blocks being in contact with the top ends of the mechanical lifting members, (d) operating each mechanical lifting member to retract for a first distance, so that the caisson structure is sinked for the same distance; (e) separating all the mechanical lifting members into a first group and a second group which are staggered, operating the first group to retract for a second distance, so that the second group receiving the whole load of the caisson structure, taking out the uppermost heel blocks in the position-limiting walls corresponding to the first group of the mechanical lifting members, operating the first group to extend until the remaining heel blocks being in contact with base portions of the external support blocks, cutting away a length of the position-limiting walls at their bottom, then operating the second group to retract for a third distance, so that the first group receiving the whole load of the caisson structure, taking out the uppermost heel blocks in the position-limiting walls corresponding to the second group of the mechanical lifting members, operating the second group to extend until the remaining heel blocks being in contact with base portions of the external support blocks, cutting away a length of the position-limiting walls at their bottom; (f) repeating steps (d) and (e) until the caisson structure is sinked to a predetermined position; (g) operating the first group to retract for a forth distance so that the second group receiving the whole load of the caisson structure, then taking out the first group and casting cap concrete between the caisson structure and the support piles under the first group of the mechanical lifting members, and operating the second group to retract for a fifth distance so that the cap concrete receiving the whole load of the caisson structure, then taking out the second group and casting another amount of cap concrete between the caisson structure and the support piles under the second group of the mechanical lifting members.
 17. The method of claim 16, wherein in the step (c) a guiding rail is provided on the external surfaces of the well walls between the position-limiting walls.
 18. The method of claim 17, wherein in the step (c) a position-limiting plate is provided outside the position-limiting wells, the position-limiting plate, the position-limiting wells and the guiding rail constituting a position-limiting device enabling the heel blocks to move only in a vertical direction.
 19. A method for precisely sinking a caisson structure into ground, comprising: step S1: selecting a construction area, and driving support piles into the ground within the area with a length of the support piles exposed above the ground; step S2: placing a mechanical lifting member on each support pile, these mechanical lifting members being initially in a extended position; step S3: placing a caisson structure on the mechanical lifting members, said caisson structure including enclosed well walls and frame beams provided inside and fixed to the well walls, a first portion of the support piles being on the inner side of the well walls, a second portion of the support piles being on the outer side of the well walls, external support blocks being provided on the external surfaces of the well walls, the external support blocks comprising a base portion and a pair of position-limiting walls extending downward at the base portion, a plurality of heel blocks being provided in the position-limiting walls with one heel block above another, each mechanical lifting member being supported by one corresponding support pile, the bottom sides of the frame beams being supported by the first portion of the support piles, and the lowest heel blocks being supported by the second portion of the support piles; step S4: operating each mechanical lifting member to retract for a first distance, so that the caisson structure is sinked for the same distance; step S5: separating all the mechanical lifting members into a first group and a second group which are staggered, operating the first group to retract for a second distance, so that the second group receiving the whole load of the caisson structure, cutting away at its top end a length of each of the first portion of the support file under the first group of the mechanical lifting members and taking out the uppermost heel blocks in the position-limiting walls corresponding to the first group of the mechanical lifting members, operating the first group to extend to support between the first portion of the support piles and the frame beams or until the remaining heel blocks being in contact with base portions of the external support blocks, cutting away a length of the position-limiting walls at their bottom, then operating the second group to retract for a third distance, so that the first group receiving the whole load of the caisson structure, cutting away at its top end a length of each of the second portion of the support file under the second group of the mechanical lifting members and taking out the uppermost heel blocks in the position-limiting walls corresponding to the second group of the mechanical lifting members, operating the second group to extend to support between the second portion of the support piles and the frame beams or until the remaining heel blocks being in contact with base portions of the external support blocks, cutting away a length of the position-limiting walls at their bottom; step S6: repeating steps S4 and S5 until the caisson structure is sinked to a predetermined position; step S7: operating the first group to retract for a forth distance so that the second group receiving the whole load of the caisson structure, then taking out the first group and casting cap concrete between the frame beams or the base portions of the external support blocks and the support piles under the first group of the mechanical lifting members, and operating the second group to retract for a fifth distance so that the cap concrete receiving the whole load of the caisson structure, then taking out the second group and casting another amount of cap concrete between the frame beams or the base portions of the external support blocks and the support piles under the second group of the mechanical lifting members.
 20. The method of claim 19, wherein in the step S3 internal support blocks are provided on internal surfaces of the well walls close to the bottom of the caisson structure, the internal support blocks extending inward and perpendicularly to the internal surfaces, and the mechanical lifting members been supported by the first portion of the support piles, thus in the step S7 the cap concrete is located between the internal support blocks and the first portion of the support piles.
 21. The method of claim 19, wherein in the step S3 a guiding rail is provided on the external surfaces of the well walls between the position-limiting walls.
 22. The method of claim 21, wherein in the step S3 a position-limiting plate is provided outside the position-limiting wells, the position-limiting plate, the position-limiting wells and the guiding rail constituting a position-limiting device enabling the heel blocks to move only in a vertical direction. 